Compounds having the formula ##STR1## wherin R, R.sup.1 and R.sup.2 are as hereinafter defined, are known to induce growth regulating responses in plants, which responses are exemplified but not necessarily limited to ethylene or ethylene-type responses. It is known that ethylene and other gases affect the growth cycle of plants, although the mechanism of this effect is not fully understood. The phosphonic acid compounds generically represented by the formula shown above contain in their structures molecular configurations which are capable of forming ethylene or like compounds.
Plant growth regulators such as phosphonic acid are commonly used to regulate growth of small grain plants such as barley and wheat. Growth of such plants is regulated by applying the plant growth regulator during the growth stage between emergence of flag leaf and boot swelling. This stage is also described as early to late boot stage. Plant growth regulators are not commonly used to regulated growth of rice crops plants.
Fritz et al., U.S. Pat. Nos. 3,879,188, 4,374,661 and 4,401,454, all describe a growth regulation process involving application of certain phosphonic acid compounds having the general formula ##STR2## where R is selected from the group consisting of haloethyl and phosphono-ethyl; and
R.sub.1 and R.sub.2 are selected from the group consisting of PA1 (a) chlorine, hydroxy, and salts thereof; PA1 (b) the group --OR.sub.3 and the group --O--CH.sub.2 R.sub.3 where each R' is one member of the group of unsubstituted aryl, substituted aryl and heterocyclic groups; PA1 (c) the group --OR.sub.3 and the group --O--CH.sub.2 R.sub.3 where each R.sub.3 is a different member of the group of hydrogen, unsubstituted alkyl, substituted alkyl, unsubstituted aryl, substituted aryl, heterocycle, alkene and alkyne, provided that when one R.sub.3 is selected from the group of unsubstituted alkyl, substituted alkyl, alkene and alkyne, the other R.sub.3 is selected from the group of unsubstituted aryl, substituted aryl and heterocycle; PA1 (d) together R.sub.1 and R.sub.2 represent the group ##STR3## where one of R.sub.4 and R.sub.5 is --O-- and the other is selected from the group of --O--, --OCH.sub.2, --CO--O--and CONH, and R.sub.6 represents a cyclic group selected from the group consisting of phenyl, substituted phenyl, heterocyclic ring and substituted heterocyclic ring; (e) one of R.sub.1 and R.sub.2 is --OR.sub.7 and the other is ##STR4## wherein each R.sub.7 is the same or different and is selected from the group of hydrogen, unsubstituted alkyl, substituted alkyl, unsubstituted aryl, substituted aryl and a heterocycle group, and wherein R is as previously defined. A preferred phosphonic derivative according to Fritz et al. is 2-chloroethyl phosphonic acid. This preferred derivative is claimed to be useful in hastening ripening in unpicked fruit. PA1 R.sup.1 and R.sup.2 are selected from PA1 (a) chlorine, hydroxy, and salts thereof; PA1 (b) the group --OR.sup.3 and the group --O--CH.sub.2 R.sup.3 wherein each R.sup.3 is a member of the group of unsubstituted aryl, substituted aryl and heterocyclic groups; PA1 (c) the group --OR.sup.3 and the group --O--CH.sub.2 R.sup.3 wherein each R.sup.3 is a different member of the group of hydrogen, unsubstituted alkyl, substituted alkyl, unsubstituted aryl, substituted aryl, heterocyclic, alkenyl and alkynyl with the proviso that when one R.sup.3 is selected from the group of unsubstituted alkyl, substituted alkyl, alkenyl and alkynyl, the other R.sup.3 is selected from the group of unsubstituted aryl, substituted aryl and heterocycle; PA1 (d) together R.sup.1 and R.sup.2 represent ##STR7## (R.sup.4 and R.sup.5 are each connected with the phosphorous atom by a separate single bond) where one R.sup.4 and R.sup.5 is --O-- and the other is selected from the group of --O--, OCH.sub.2 --, --CO--O and CONH, and R.sup.6 represents a cyclic group selected from the group consisting of benzene, substituted benzene, heterocyclic rings and substituted hetercyclic rings; or PA1 (e) one of R.sup.1 and R.sup.2, is --OR.sup.7 and the other is: ##STR8## wherein each R.sup.7 is the same or different and is selected from the group of hydrogen, unsubstituted alkyl, substituted alkyl, unsubstituted aryl, substituted aryl and a heterocyclic group, and wherein R is as defined hereinbefore. PA1 increase in number of panicles per unit land area; PA1 increase in number of panicles per plant; PA1 increase in grain weight; PA1 increase in number of grains per panicle; PA1 increase in plant height; PA1 increase in straw stiffness; and PA1 reduction in number of sterile florets per panicle.
Jacques, U.S. Pat. No. 3,896,163, describes a purification process for separating an aliphatic phosphonic acid such as 2-chloroethyl phosphonic acid from its corresponding half-ester.
Hayakawa et al., U.S. Pat. No. 4,152,429, describe a method for controlling plant fungi and regulating plant growth comprising applying to the plant a composition comprising 2-chloroethyl phosphonic acid and a conventional agricultural fungicide.
Fritz et al., U.S. Pat. No. 4,240,819, describe a method for inhibiting plant growth which comprises applying thereto an effective amount of 2-chloroethyl phosphonic acid.
Fritz et al., U.S. Pat. No. 4,352,689, describe a method for controlling apical dominance which comprises applying to crops an effective amount of 2-chloroethyl phosphonic acid, ranging from about 0.2 lb to about 16 lbs per acre.
Ethephon is the generic name for 2-chloroethyl phosphonic acid marketed under ETHREL.RTM., PREP.TM., CERONE.RTM., and FLOREL.TM. trademarks Ethephon, upon decomposition by a simple base catalyzed reaction, releases ethylene gas. The release of ethylene increases with increasing solution pH. When ethephon is applied to higher plants, ethylene is released in plant cells by the following chemical reaction: ##STR5##
Ethylene is one of the 5 commonly recognized classes of naturally occurring plant hormones, i.e. Auxins, Gibberellins, Cytokinins, Abscisic acid, and Ethylene. Ethylene is known to play an important regulatory role in various physiological processes, from germination through senescence. Ethephon in liquid form provides a convenient means of ethylene application to plants and is widely used in research for studying ethylene-mediated processes.
Chaudhuri, D., et al., Indian Agriculturist, vol 24, pp. 169-175 (1980) describe rice yield increase with foliar application of ethephon or other plant growth regulators at tillering, booting or panicle initiation stages.
Fang, B. C. et al., Shanghai Agricultural Science and Technology, vol. 5, pp. 11-12 (1982) and Fang, B. C. et al., Acta Botanica Sinica, vol 25, pp. 344-351 (1983) describe rice yield increase with application of ethephon to seedlings of double-cropping second season rice at the 5-leaf stage.
Chaudhuri, D. et al. and Fang et al. do not teach rates of application of ethephon and do not distinguish among the various growth stages of tillering, booting and panicle initiation. The present invention teaches a method for increasing rice crop yield by applying a phosphonic acid plant growth regulator at specific application rates and at a specific Plant growth stage.
It is an object of this invention to increase rice grain yield by applying phosphonic acid growth regulators at specific rates and particular stages of plant growth. It is a further object of the present invention to increase the number of seeds and seed producing tillers of a rice crop by applying phosphonic acid growth regulators at rates and plant growth stages which result in manipulation of certain plant physiological processes.